Method for determining iron phosphide in phosphate positive electrode material, positive electrode material and application

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to a method for determining iron phosphide in a phosphate positive electrode material, the positive electrode material and application. Comprising the following steps: preparing standard solutions of a series of phosphate positive electrode materials with different iron phosphide contents; respectively collecting and purifying magnetic substances in the standard solutions, and adding a quimocilidone reagent to determine the corresponding quinoline phosphomolybdate precipitate; drawing a standard curve according to the mass of the iron phosphide and the mass of the quinoline phosphomolybdate precipitate in the standard solutions with different iron phosphide contents; preparing a to-be-detected solution, collecting and purifying magnetic substances in the to-be-detected solution, adding a quinmolybdenum citronone reagent to determine the mass of the quinoline phosphomolybdate precipitate, and calculating the content of iron phosphide in the to-be-detected phosphate positive electrode material. By means of the method, the content of trace iron phosphide in the phosphate positive electrode material can be efficiently, accurately and quantitatively analyzed, the content of iron phosphide in the phosphate positive electrode material can be quantitatively regulated and reduced, and the electrochemical performance of the phosphate positive electrode material is improved.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, and in particular relates to a method for determining iron phosphide in phosphate-based cathode materials, cathode materials and their applications. Background Technology

[0002] Phosphate-based cathode materials, such as lithium iron phosphate, have become one of the most ideal cathode materials in the field of power batteries due to their excellent thermal stability, good cycle life, electrochemical stability, and environmental friendliness. However, the industrial application of phosphate-based cathode materials requires scale-up experiments, which inevitably introduces impurities. Generally, the introduction of inactive impurities not only leads to a decrease in the specific capacity and energy density of the material, but also, when the impurities contain metallic magnetic impurities, can seriously damage the battery's lifespan and safety.

[0003] During the sintering process for preparing phosphate-based cathode materials, Fe2P impurity phase is generated. Fe2P is magnetic, and its presence reduces the ionic conductivity of phosphate-based cathode materials, resulting in a decrease in capacity and cycle stability, and also has a significant impact on battery safety performance.

[0004] Therefore, it is particularly important to find a method to determine trace amounts of Fe2P in phosphate-based cathode materials. By monitoring the content of Fe2P impurity phase in phosphate-based cathode materials, the content of Fe2P impurity phase in phosphate-based cathode materials can be quantitatively controlled and reduced. Summary of the Invention

[0005] The purpose of this application is to provide a method for determining iron phosphide in phosphate-based cathode materials, the cathode material itself, and its application, aiming to solve to some extent the problem that the content of iron phosphide in existing phosphate-based cathode materials is difficult to measure accurately.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application provides a method for determining iron phosphide in a phosphate-based cathode material, comprising the following steps:

[0008] Prepare a series of standard solutions of phosphate-based cathode materials with different iron phosphide contents;

[0009] The magnetic substances in the standard solutions were collected and purified separately. After digestion of the magnetic substances in the standard solutions, quinoline phosphomolybdate reagent was added to carry out a precipitation reaction to obtain the quinoline phosphomolybdate precipitate in the standard solutions.

[0010] A standard curve was plotted based on the mass of ferric phosphide in the standard solutions with different ferric phosphide contents and the mass of quinoline phosphomolybdate precipitate in the standard solutions.

[0011] A test solution containing the phosphate-based cathode material to be tested was prepared. The magnetic substances in the test solution were collected and purified. After digesting the magnetic substances in the test solution, quinoline phosphomolybdate reagent was added to carry out a precipitation reaction to obtain the quinoline phosphomolybdate precipitate in the test solution.

[0012] The mass of quinoline phosphomolybdate precipitate in the test solution was determined, and the content of iron phosphide in the phosphate-based cathode material was calculated based on the standard curve.

[0013] In some implementations, the standard solution contains phosphate-based cathode material without phosphate, ferric phosphate, dispersant, and demagnetizing water.

[0014] In some implementations, the test solution contains the phosphate-based cathode material to be tested, a dispersant, and demagnetizing water.

[0015] In some implementations, the concentration and type of the phosphate-based cathode material to be tested in the test solution are the same as the concentration and type of the phosphate-based cathode material in the standard solution.

[0016] In some implementations, the conditions for determining the phosphomolybdate quinoline precipitate in the test solution are the same as those for determining the phosphomolybdate quinoline precipitate in the standard solution.

[0017] In some implementations, the standard solutions are prepared with at least five iron phosphide concentration gradients.

[0018] In some implementations, the concentration of ferric phosphide in the standard solution is 0.00025 g / L to 0.015 g / L.

[0019] In some implementations, the concentration and type of dispersant in the test solution are the same as those in the standard solution.

[0020] In some implementations, the dispersant in the standard solution and the test solution includes at least one of sodium dodecyl sulfate, vinylpyrrolidone, hexadecyltrimethylammonium bromide, and Huntsman X-3204.

[0021] In some implementations, the concentration of the dispersant in the standard solution and the test solution is 0.36 g / L to 0.5 g / L.

[0022] In some implementations, the concentration of the phosphate-free iron phosphate cathode material in the standard solution is 0.198 kg / L to 0.22 kg / L.

[0023] In some implementations, the concentration of the phosphate-based cathode material to be tested in the test solution is 0.198 kg / L to 0.22 kg / L.

[0024] In some implementations, the phosphate-based cathode material and the phosphate-based cathode material to be tested include at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium titanium phosphate, lithium manganese phosphate, lithium manganese iron titanium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0025] In some implementations, the step of collecting and purifying the magnetic material in the standard solution or the test solution includes: using a magnetic rod to adsorb the standard solution or the test solution, collecting the magnetic material adsorbed on the surface of the magnetic rod, and sequentially performing magnetic separation and washing treatments to obtain the magnetic material in the standard solution or the test solution.

[0026] In some implementations, the step of digesting the magnetic material in the standard solution or the test solution includes: dissolving the magnetic material in an acidic solution under heating conditions.

[0027] In some implementations, when determining the quinoline phosphomolybdate precipitate in the standard solution or the test solution, the temperature conditions for the precipitation reaction are 200℃~220℃.

[0028] In some implementations, the standard curve is plotted with the mass of iron phosphide on the x-axis and the mass of quinoline phosphomolybdate precipitate on the y-axis.

[0029] In some implementations, the magnetic rod is a magnetic rod wrapped in heat-shrink tubing. After the adsorption treatment, the magnetic rod wrapped in heat-shrink tubing is disassembled, and the magnetic material on the surface of the heat-shrink tubing is collected.

[0030] In some implementations, the stirring speed of the adsorption treatment is 50 rpm to 70 rpm, and the stirring time is 25 min to 35 min.

[0031] In some implementations, the magnetic separation process includes the steps of: using a magnetic block to perform non-contact sorting of the collected magnetic material to separate and remove the phosphate-based cathode material.

[0032] In some implementations, the washing process includes the step of washing the magnetic material after magnetic separation with dilute hydrochloric acid at a concentration of 4% to 6% to separate and remove the phosphate-based cathode material.

[0033] In some implementations, the concentration of nitric acid in the acidic solution is 25%–30%, and the concentration of hydrochloric acid is 4%–10%.

[0034] In some implementations, the volume ratio of the acidic solution to the quinomolybdate reagent is (18 mL to 25 mL): (28 mL to 33 mL).

[0035] In some implementations, the temperature of the heating condition is 200℃~240℃.

[0036] In some implementations, the magnetic rod is selected from the 11000GS to 12000GS model.

[0037] In some implementations, the heat-shrink tubing wrapped around the magnetic rod is made of at least one of polypropylene, polyvinyl fluoride, ethylene propylene diene monomer (EPDM), and polytetrafluoroethylene (PTFE).

[0038] In some implementations, the acidic solution includes aqua regia and water in a volume ratio of 1:1.

[0039] In some implementations, the linear correlation coefficient R of the standard curve 2 Not less than 0.999.

[0040] Secondly, this application provides a cathode material containing a phosphate-based cathode material. After determining the iron phosphide content using the above method, the iron phosphide content in the phosphate-based cathode material is adjusted.

[0041] In some implementations, the content of iron phosphide in the phosphate-based cathode material is not higher than 5 ppm;

[0042] In some implementations, the method for controlling the iron phosphide content in the phosphate-based cathode material includes at least one of: controlling process conditions, physical adsorption removal, and chemical dissolution removal.

[0043] Thirdly, this application provides an application of a positive electrode material, which is applied to a positive electrode sheet and / or a secondary battery.

[0044] The method for determining iron phosphide in phosphate-based cathode materials provided in the first aspect of this application involves preparing a series of standard solutions of phosphate-based cathode materials with different iron phosphide contents. Magnetic substances in the standard solutions are collected and purified, digested, and then quinomolybdate reagent is added to convert the magnetic substances into quinoline phosphomolybdate precipitate. This effectively amplifies the iron phosphide content in the standard solutions and improves the accuracy of capturing trace amounts of iron phosphide in the test samples. A standard curve is plotted based on the mass of iron phosphide in the standard solutions with different iron phosphide contents and the mass of the quinoline phosphomolybdate precipitate. Using the phosphate-based cathode material to be tested as the test object, a test solution is prepared, and the magnetic substances in the test solution are collected and purified. After digesting the magnetic substances in the test solution, quinomolybdate reagent is added to induce a precipitation reaction, resulting in quinoline phosphomolybdate precipitate in the test solution. The mass of the corresponding quinoline phosphomolybdate precipitate in the test solution is determined according to the method for determining quinoline phosphomolybdate precipitate in the standard curve. Substituting this mass into the standard curve allows for the calculation of the iron phosphide content in the phosphate-based cathode material to be tested. The method described in this application enables efficient and accurate quantitative analysis of trace amounts of iron phosphide in phosphate-based cathode materials. Based on this, it is beneficial to quantitatively control and reduce the content of Fe2P impurity phase in phosphate-based cathode materials, thereby reducing the impact of iron phosphide on the ionic conductivity, capacity, cycle stability, and other properties of phosphate-based cathode materials and improving their electrochemical performance.

[0045] The cathode material provided in the second aspect of this application includes a phosphate-based cathode material. After determining the iron phosphide content of the phosphate-based cathode material using the above method, the content of Fe2P impurity phase in the phosphate-based cathode material is quantitatively controlled and reduced, thereby reducing the influence of iron phosphide on the ionic conductivity, capacity, cycle stability and other properties of the phosphate-based cathode material, and improving the electrochemical performance of the phosphate-based cathode material.

[0046] The phosphate-based cathode material provided in this application has high conductivity, capacity, and cycle stability. It can be directly applied to cathode sheets or further applied to secondary batteries to improve the energy density, cycle stability, and other electrochemical performance of cathode sheets and secondary batteries. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic flowchart of the method for determining iron phosphide in phosphate-based cathode materials provided in the embodiments of this application;

[0049] Figure 2 This is a photograph of a magnetic rod wrapped in heat shrink tubing, as provided in an embodiment of this application.

[0050] Figure 3 It is the standard curve provided in Embodiment 1 of this application;

[0051] Figure 4 This is the standard curve provided in Embodiment 4 of this application;

[0052] Figure 5 This is the standard curve provided in Comparative Example 1 of this application;

[0053] Figure 6 This is a comparison graph of the fitting of the standard curves provided in Embodiments 1, 4 and Comparative Example 1 of this application. Detailed Implementation

[0054] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0055] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0056] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0057] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0058] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0059] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass mentioned in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0060] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0061] The first aspect of this application provides a method for determining iron phosphide in phosphate-based cathode materials, as shown in the attached figure. Figure 1 As shown, it includes the following steps:

[0062] S10. Prepare a series of standard solutions of phosphate-based cathode materials with different iron phosphide contents;

[0063] S20. Collect and purify the magnetic substances in the standard solutions separately; after digesting the magnetic substances in the standard solutions, add quinomolybdate reagent to carry out a precipitation reaction to obtain quinoline phosphomolybdate precipitate in the standard solutions;

[0064] S30. Plot a standard curve based on the mass of ferric phosphide in standard solutions with different ferric phosphide contents and the mass of quinoline phosphomolybdate precipitate in the standard solutions.

[0065] S40. Prepare a test solution containing the phosphate-based cathode material to be tested, collect and purify the magnetic material in the test solution, digest the magnetic material in the test solution, add quinoline phosphomolybdate reagent to carry out a precipitation reaction, and obtain quinoline phosphomolybdate precipitate in the test solution.

[0066] S50. Determine the mass of quinoline phosphomolybdate precipitate in the test solution and calculate the iron phosphide content in the phosphate-based cathode material to be tested based on the standard curve.

[0067] The method for determining iron phosphide in phosphate-based cathode materials provided in the first aspect of this application involves preparing a series of standard solutions with different iron phosphide contents, collecting and purifying magnetic substances in the standard solutions, digesting the magnetic substances, and adding quinomolybdate reagent to convert the magnetic substances into quinoline phosphomolybdate precipitate. This effectively amplifies the iron phosphide content in the standard solutions and improves the accuracy of capturing trace amounts of iron phosphide in the test samples. A standard curve is plotted based on the mass of iron phosphide in the standard solutions with different iron phosphide contents and the mass of quinoline phosphomolybdate precipitate. Using the phosphate-based cathode material to be tested as the test object, a test solution is prepared, and the magnetic substances in the test solution are collected and purified. After digesting the magnetic substances in the test solution, quinomolybdate reagent is added to carry out a precipitation reaction, resulting in quinoline phosphomolybdate precipitate in the test solution. The mass of the corresponding quinoline phosphomolybdate precipitate in the test solution is measured according to the method for determining quinoline phosphomolybdate precipitate in the standard curve. Substituting this mass into the standard curve, the iron phosphide content in the phosphate-based cathode material to be tested can be calculated. The method described in this application can efficiently and accurately analyze the content of trace amounts of iron phosphide in phosphate-based cathode materials. Based on this, it is beneficial to quantitatively control and reduce the content of Fe2P impurity phase in phosphate-based cathode materials, reduce the impact of iron phosphide on the ionic conductivity, capacity, cycle stability and other properties of phosphate-based cathode materials, and improve the electrochemical performance of phosphate-based cathode materials.

[0068] In step S10 above: the standard solution contains phosphate-based cathode material without phosphate, ferric phosphate, dispersant and demagnetizing water. A standard solution containing phosphate-based cathode material without phosphate, ferric phosphate, dispersant and demagnetizing water is prepared. The phosphate-based cathode material without phosphate and the additional ferric phosphate are used as standard test samples of the phosphate-based cathode material to be tested. A dispersant is added to improve the dispersion performance of the raw material components. By adding different amounts of ferric phosphate, standard solutions with different ferric phosphate contents are obtained.

[0069] In some possible implementations, standard solutions with at least five ferric phosphide concentration gradients are prepared; specifically, standard solutions with 5, 6, 7, 8, 9, or 10 ferric phosphide concentration gradients can be prepared. This improves the accuracy of the standard curve. Furthermore, the selected concentration range should cover the possible concentration range of the analyte in the sample. The concentration gradients should be evenly distributed, avoiding excessive density or sparseness within any concentration range. Overly dense gradients may lead to data redundancy, while overly sparse gradients may fail to adequately reflect the trend of the curve.

[0070] In some possible implementations, the concentration of iron phosphide in the standard solution is 0.00025 g / L to 0.015 g / L. Generally, 1 kg of phosphate-based cathode material samples contains 0.004 g, or 4 ppm, of iron phosphide, and sometimes only a small amount, around 1 ppm. The higher the sintering temperature of lithium iron phosphate, the higher the iron phosphide content. Therefore, the iron phosphide concentration range in the standard solution prepared in this application covers the range of iron phosphide content in the tested phosphate-based cathode material.

[0071] In some specific embodiments, standard solutions with iron phosphide concentrations of 0.00025 g / L, 0.0005 g / 5 L, 0.001 g / L, 0.003 g / L, 0.005 g / L, 0.007 g / L, 0.010 g / L, and 0.015 g / L were prepared. This approach is more conducive to improving the accuracy of the standard curve.

[0072] In some possible implementations, the concentration of the phosphate-free iron phosphate cathode material in the standard solution is between 0.198 kg / L and 0.22 kg / L. This is advantageous for improving the accuracy of the test. For example, the concentration of the phosphate-free iron phosphate cathode material in the standard solution can be any typical but non-limiting point value or a range between any two point values, such as 0.198 kg / L, 0.20 kg / L, 0.21 kg / L, or 0.22 kg / L.

[0073] In some possible implementations, the dispersant in the standard solution includes at least one of sodium dodecyl sulfate, vinylpyrrolidone, hexadecyltrimethylammonium bromide, and Huntsman X-3204. These dispersants can all improve the dissolution and dispersion stability of phosphate-based cathode materials in aqueous solutions, which is beneficial for the thorough detection of iron phosphide in the sample. In some specific embodiments, sodium dodecyl sulfate is included as the dispersant; at the same addition amount, sodium dodecyl sulfate provides the best dispersing effect and is also inexpensive.

[0074] In some possible implementations, the concentration of the dispersant in the standard solution is 0.36 g / L to 0.5 g / L. This ensures good dispersion of the raw material components while avoiding excessive bubble formation due to excessive dispersant addition, which could increase errors during the extraction of magnetic materials. For example, the concentration of the dispersant in the standard solution can be any typical but non-limiting point value or a range between any two point values, such as 0.36 g / L, 0.37 g / L, 0.38 g / L, 0.40 g / L, 0.41 g / L, 0.42 g / L, 0.43 g / L, 0.44 g / L, 0.45 g / L, 0.46 g / L, 0.48 g / L, 0.49 g / L, or 0.5 g / L.

[0075] Among the possible implementations, iron phosphate-based cathode materials without phosphate are preferably carbon-coated, as carbon coating improves the structural stability and electronic conductivity of the cathode material. Iron phosphate-based cathode materials without phosphate can be prepared in-house by extracting magnetic materials using a magnetic rod, preparing a cleanliness film, and then using EDS (energy dispersive spectroscopy) to confirm the absence of iron phosphate; alternatively, they can be commercially purchased directly.

[0076] Among some possible implementations, phosphate-based cathode materials without iron phosphate include at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium titanium phosphate, lithium manganese phosphate, lithium manganese iron titanium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. These phosphate-based cathode materials currently have high application prospects. Moreover, these cathode materials often readily produce iron phosphate during the sintering process, making accurate quantitative analysis of the iron phosphate content in these cathode materials of greater practical significance.

[0077] In step S20 above:

[0078] In some possible implementations, the steps for collecting and purifying magnetic substances in the standard solution include: adsorbing the standard solution onto a magnetic rod, collecting the adsorbed magnetic substances on the surface of the magnetic rod, and then performing magnetic separation and washing to obtain the magnetic substances in the standard solution. In this case, using a magnetic rod to adsorb and collect the magnetic substances in the solution, followed by separation and washing to remove impurities, helps improve the accuracy of subsequent analyses.

[0079] In some possible implementations, the magnetic rod is wrapped in heat-shrink tubing. After adsorption treatment, the heat-shrink tubing is removed from the magnetic rod, and the magnetic material on the surface of the tubing is collected. In this case, using heat-shrink tubing to wrap the magnetic rod prevents it from directly contacting the material, ensuring that the extracted magnetic material is adsorbed onto the heat-shrink tubing on the surface of the magnetic rod. After adsorption and extraction, the magnetic rod is removed, and the heat-shrink tubing is ultrasonically cleaned to obtain an aqueous solution of the magnetic material. This method ensures the adsorption and extraction of the magnetic material while reducing its loss, thus improving the accuracy of the collection and subsequent analysis.

[0080] In some possible implementations, the heat-shrink tubing wrapped around the magnetic rod is made of at least one of the following materials: PVC (polypropylene), PVDF (polyvinyl fluoride), EPDM (ethylene propylene diene monomer), and PTFE (polytetrafluoroethylene). In this case, the material of the heat-shrink tubing can be heated and shrunk, better conforming to the shape and size of the magnetic rod, and is less prone to breakage during stirring.

[0081] In some specific embodiments, the heat shrink tubing is directly sleeved on the outside of the magnetic rod, completely enclosing the magnetic rod and preventing magnetic materials from being directly adsorbed onto the magnetic rod.

[0082] In some possible implementations, the magnetic rods are selected from 11000GS to 12000GS; where GS is an abbreviation for Gauss, the unit of Gaussian magnetic induction intensity, used to measure the strength of a magnetic field. Magnetic rods of 11000GS to 12000GS refer to magnetic rods made of high-performance magnetic materials (such as neodymium iron boron), whose surfaces can generate strong magnetic fields, exhibiting excellent adsorption and extraction effects on magnetic substances in standard solutions and test solutions.

[0083] In some possible implementations, the stirring speed for adsorption treatment is 50 rpm to 70 rpm, and the stirring time is 25 min to 35 min. In this case, the adsorption and extraction of magnetic substances from the solution by the magnetic rod can be sufficiently ensured. For example, the stirring speed for adsorption treatment can be any typical but non-limiting value such as 50 rpm, 55 rpm, 60 rpm, 65 rpm, or 70 rpm, or a range between any two values; the stirring time can be any typical but non-limiting value such as 25 min, 28 min, 30 min, 33 min, or 35 min, or a range between any two values.

[0084] In some specific embodiments, the magnetic rod is a magnetic rod wrapped in heat shrink tubing, as shown in the attached image. Figure 2 As shown, after adsorption treatment of the standard solution, the magnetic rod with heat-shrink tubing was removed and placed in a clean beaker. The magnetic rod was then removed from the heat-shrink tubing, and the tubing was cut into three equal parts with ceramic scissors. Demagnetizing water was added to the beaker, covering the heat-shrink tubing, and ultrasonic cleaning was performed for 5 minutes. After cleaning, deionized water was used to rinse the magnetic material on the heat-shrink tubing into the beaker, while simultaneously scraping off the magnetic material with a ceramic knife. The rinsed heat-shrink tubing was then placed in another beaker, water was added to cover the tubing, and ultrasonic cleaning was performed for 5 minutes. This process was repeated. The mixture of magnetic material and water in all beakers was slowly poured into another beaker to obtain the initially collected magnetic material. At this point, the initially collected magnetic material also contained stainless steel and a small amount of iron oxide, requiring further magnetic separation and washing purification.

[0085] In some possible implementations, magnetic separation includes the steps of: using magnetic blocks to perform non-contact sorting of the collected magnetic materials, separating and removing phosphate-based cathode materials. Non-contact sorting means that the magnetic blocks do not directly contact the magnetic materials, reducing the loss of magnetic materials. Magnetic separation is used to enrich the magnetic materials and also to wash away excess lithium iron phosphate.

[0086] In some embodiments, the magnetic material aqueous solution in all beakers is slowly poured into another beaker to obtain the initially collected magnetic material, which is then magnetically separated at the bottom of the beaker using a magnetic block.

[0087] In some possible implementations, the washing process includes the step of washing the magnetic material after magnetic separation with a dilute hydrochloric acid solution of 4% to 6% to separate and remove the phosphate-based cathode material. In this case, the dilute hydrochloric acid is used to wash the magnetic material to remove excess impurities such as lithium iron phosphate, while avoiding excessive acid concentration that could consume the magnetic material. Exemplarily, the concentration of the dilute hydrochloric acid can be any typical but non-limiting value such as 4%, 5%, or 6%, or a range between any two values.

[0088] In some possible implementations, the digestion step of the magnetic material includes: dissolving the magnetic material in an acidic solution, preferably a strong acid solution, under heating conditions. In this case, the ferric phosphide magnetic material has good stability and requires a strong acid for complete dissolution, which is beneficial for subsequent precipitation reaction with quinomolybdate reagent to obtain quinoline phosphomolybdate precipitate.

[0089] In some possible implementations, the heating temperature is between 200°C and 240°C. Under this heating condition, the efficiency of acid digestion of magnetic materials can be improved. For example, the heating temperature can be any typical but non-limiting point value or a range between any two point values, such as 200°C, 210°C, 220°C, 230°C, or 240°C.

[0090] In some possible implementations, the concentration of nitric acid in the acidic solution is 25%–30%, and the concentration of hydrochloric acid is 4%–10%. In this case, the acidic solution can thoroughly and completely digest the magnetic material with high digestion efficiency. For example, the concentration of nitric acid in the acidic solution can be any typical but non-limiting value or a range between any two values, such as 25%, 26%, 27%, 28%, 29%, or 30%, and the concentration of hydrochloric acid can be any typical but non-limiting value or a range between any two values, such as 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0091] In some possible implementations, the acidic solution includes aqua regia and water in a 1:1 volume ratio, denoted as aqua regia (1+1). Here, aqua regia refers to a solution with a concentrated nitric acid to concentrated hydrochloric acid volume ratio of 3:1. Using aqua regia (1+1), the volume ratio of aqua regia to water is 1:1. In this case, the concentration of nitric acid in aqua regia (1+1) is 25.5%, and the concentration of hydrochloric acid is 4.5%. In this configuration, aqua regia (1+1) can completely dissolve magnetic substances and convert phosphorus (P) into phosphate ions.

[0092] In some possible implementations, after digesting the magnetic material, a quinomolybdate reagent is added to induce a precipitation reaction at a temperature of 200°C to 220°C. This enhances the precipitation reaction between the magnetic material digestion solution and the quinomolybdate reagent, resulting in quinoline phosphomolybdate precipitate. The quinomolybdate reagent reacts with phosphate ions to form a precipitate, and the mass of iron phosphide is calculated from the mass of the precipitate. The generated quinoline phosphomolybdate precipitate amplifies the mass of iron phosphide by 15.5 times, improving the accuracy of testing for trace amounts of iron phosphide in the sample. For example, the precipitation reaction temperature can be any typical but non-limiting point value or a range between any two points, such as 200°C, 205°C, 210°C, 215°C, or 220°C.

[0093] In some possible implementations, the quinomolybdate reagent is prepared according to national standards. In some specific embodiments, the specific preparation of the quinomolybdate reagent and its reaction with the sample can be referenced to the national standard GB / T1871.1-1995.

[0094] In some embodiments, after digesting the magnetic material, water is added to 100 mL, and the mixture is heated to boiling at 200°C to 220°C. Quinomolybdate reagent is then added to react and generate a precipitate.

[0095] In some possible implementations, the volume ratio of acidic solution to quinoline phosphomolybdate reagent is (18 mL to 25 mL): (28 mL to 33 mL); in this case, it is beneficial to improve the efficiency of precipitating quinoline phosphomolybdate.

[0096] For example, after digesting the magnetic material with acidic solutions of 18 mL, 19 mL, 20 mL, 21 mL, 22 mL, 23 mL, 24 mL, and 25 mL, water is added to bring the volume to 100 mL. Then, 28 mL, 29 mL, 30 mL, 31 mL, 32 mL, and 33 mL of quinomolybdate reagent are added at any typical but non-limiting point value or any interval between two point values ​​to carry out a precipitation reaction and obtain quinoline phosphomolybdate precipitate.

[0097] In some possible implementations, after the precipitation reaction is complete, the quinoline phosphomolybdate precipitate is filtered using a sand core crucible, transferred to an oven at 250°C and dried for 30 min, and the precipitate mass is calculated after cooling.

[0098] In step S30 above: a standard curve is plotted based on the linear relationship between the mass of ferric phosphide and the mass of quinoline phosphomolybdate precipitate in standard solutions with different ferric phosphide contents.

[0099] In some possible implementations, the standard curve is plotted with the mass of iron phosphide on the x-axis and the mass of quinoline phosphomolybdate precipitate on the y-axis.

[0100] In some possible implementations, the linear correlation coefficient R of the standard curve 2 The correlation coefficient is not less than 0.999. The high linear correlation coefficient of the standard curves plotted in this application for the mass of iron phosphide and the mass of quinoline phosphomolybdate precipitate indicates that the smaller the deviation between the data points on the standard curve and the fitted straight line, the stronger the linear relationship between the data points and the standard curve. This strong linear relationship can more accurately reflect the relationship between the mass of iron phosphide and the mass of quinoline phosphomolybdate precipitate, thereby improving the accuracy of quantitative analysis. Furthermore, a large linear correlation coefficient of the standard curve also means that the impact of systematic and random errors on the analytical results is smaller, enabling a more accurate deduction of the iron phosphide content in the phosphate-based cathode material to be tested.

[0101] In some possible implementations, during the preparation of the standard curve, standard solutions with different iron phosphide concentrations can be measured simultaneously. After obtaining the mass data of the corresponding quinoline phosphomolybdate precipitate in the standard solutions with different iron phosphide concentrations, the standard curve can be plotted. The prepared standard curve can be reused in different embodiments.

[0102] It should be noted that, since the determination method in this application uses the linear relationship of a standard curve, the linearity coefficient R... 2 Some deviation is inevitable, but it is within the margin of error.

[0103] In step S40 above: the test solution contains the phosphate-based cathode material to be tested, a dispersant, and demagnetizing water. The test solution containing the phosphate-based cathode material to be tested, a dispersant, and demagnetizing water is prepared. Magnetic substances in the test solution are collected and purified. After digestion of the magnetic substances in the test solution, quinomolybdate reagent is added to carry out a precipitation reaction, resulting in quinoline phosphomolybdate precipitate in the test solution. That is, the mass of the corresponding quinoline phosphomolybdate precipitate in the test solution is determined according to the determination method of quinoline phosphomolybdate precipitate in the standard curve. The embodiments of this application can efficiently and accurately quantitatively analyze the Fe2P content in phosphate-based cathode materials, which helps to achieve quantitative control of Fe2P in phosphate-based cathode materials.

[0104] In some possible implementations, the dispersant in the test solution includes at least one of sodium dodecyl sulfate, vinylpyrrolidone, hexadecyltrimethylammonium bromide, and Huntsman X-3204; these dispersants can all improve the dissolution and dispersion stability of phosphate-based cathode materials in aqueous solutions, which is beneficial for the full detection of iron phosphide in the sample.

[0105] In some possible implementations, the concentration of the dispersant in the test solution is 0.36 g / L to 0.5 g / L. In this case, a good dispersion effect on the raw material components is ensured, while avoiding excessive addition of dispersant that would generate too many bubbles and increase the error in the extraction of magnetic materials.

[0106] In some possible implementations, the concentration of the phosphate-based cathode material to be tested in the test solution is 0.198 kg / L to 0.22 kg / L; in this case, it is beneficial to improve the accuracy of the test.

[0107] In some possible implementations, the phosphate-based cathode material to be tested includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium titanium phosphate, lithium manganese phosphate, lithium manganese iron titanium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. These phosphate-based cathode materials currently have high application prospects.

[0108] In some possible implementations, the phosphate-based cathode material to be tested contains about 0.004g of iron phosphide per kilogram, which is about 4ppm, or even very little about 1ppm. The higher the sintering temperature, the higher the iron phosphide content in lithium iron phosphate.

[0109] In some possible implementations, the concentration and type of the phosphate-based cathode material to be tested in the test solution are the same as the concentration and type of the iron phosphate-based cathode material without phosphide in the standard solution.

[0110] In some possible implementations, the concentration and type of dispersant in the test solution are the same as those in the standard solution.

[0111] In the embodiments described above, the test solution and the standard solution maintain the single variable of having a different source of iron phosphide, while keeping other raw material components such as the concentration and type of dispersant the same. This reduces errors caused by variables and is more conducive to improving the accuracy of the determination.

[0112] In some possible implementations, the determination conditions for quinoline phosphomolybdate precipitation in the test solution are the same as those for quinoline phosphomolybdate precipitation in the standard solution. In this case, maintaining the same determination conditions for quinoline phosphomolybdate precipitation content and performing the determination under identical conditions can better improve the accuracy of the measurement.

[0113] In some possible implementations, according to the determination method for quinoline phosphomolybdate precipitation in the standard curve, the steps for determining the mass of the corresponding quinoline phosphomolybdate precipitate in the test solution include: collecting and purifying the magnetic material in the test solution; digesting the magnetic material, adding quinoline phosphomolybdate reagent to carry out a precipitation reaction to obtain quinoline phosphomolybdate precipitate. The step of collecting and purifying the magnetic material in the test solution includes: using a magnetic rod to adsorb the test solution under the conditions of a stirring speed of 50 rpm to 70 rpm and a stirring time of 25 min to 35 min, collecting the magnetic material adsorbed on the surface of the magnetic rod, sequentially using a magnetic block to perform non-contact separation of the collected magnetic material to remove the phosphate-based cathode material, and washing the magnetic material after magnetic separation with a concentration of 4% to 6% dilute hydrochloric acid to remove the phosphate-based cathode material, thus obtaining the magnetic material. The steps for digesting magnetic materials include: dissolving the magnetic materials in a strong acid solution with a concentration of 25%–30% nitric acid and a concentration of 4%–10% hydrochloric acid under heating conditions of 200℃–240℃; and the precipitation reaction is carried out at a temperature of 200℃–220℃.

[0114] In step S50 above: the mass of quinoline phosphomolybdate precipitate in the test solution is determined, and the content of iron phosphide in the phosphate-based cathode material is calculated according to the standard curve. The embodiments of this application can efficiently and accurately quantitatively analyze the Fe2P content in phosphate-based cathode materials, which helps to achieve quantitative control of Fe2P in phosphate-based cathode materials.

[0115] In some embodiments, the mass of the measured quinoline phosphomolybdate precipitate is directly substituted into the standard curve to calculate the content of iron phosphide in the test solution, thereby calculating the content of iron phosphide in the phosphate-based cathode material to be tested.

[0116] Secondly, embodiments of this application provide a cathode material containing a phosphate-based cathode material. After determining the iron phosphide content using the above method, the iron phosphide content in the phosphate-based cathode material is adjusted.

[0117] The cathode material in this application includes a phosphate-based cathode material. After determining the iron phosphide content using the above method, the content of Fe2P impurity phase in the phosphate-based cathode material is quantitatively controlled and reduced, thereby reducing the impact of iron phosphide on the ionic conductivity, capacity, cycle stability, and other properties of the phosphate-based cathode material and improving its electrochemical performance.

[0118] In some possible implementations, the iron phosphide content in phosphate-based cathode materials is no higher than 5 ppm; in this case, phosphate-based cathode materials exhibit superior electrochemical performance, such as cycle stability.

[0119] Among some possible implementation methods, the control of iron phosphide content in phosphate-based cathode materials includes at least one of the following: controlling process conditions, physical adsorption removal, and chemical dissolution removal. Controlling process conditions can be achieved by lowering the sintering temperature, holding time, reducing carbon content (i.e., reducing the reducing atmosphere), and managing magnetic materials during production. Physical adsorption removal can involve extracting magnetic materials using magnetic rods, preparing a cleanliness membrane, and detecting the iron phosphide content using EDS (energy dispersive spectroscopy). Chemical dissolution removal can utilize the differences in solubility or reactivity of substances to separate and remove iron phosphide from the phosphate-based cathode material.

[0120] Thirdly, embodiments of this application provide an application of a positive electrode material, which is applied to a positive electrode sheet and / or a secondary battery.

[0121] The phosphate-based cathode material provided in this application has high conductivity, capacity, and cycle stability. It can be directly applied to cathode sheets or further applied to secondary batteries to improve the energy density, cycle stability, and other electrochemical performance of cathode sheets and secondary batteries.

[0122] In some possible implementations, a positive electrode is provided, comprising a current collector and a positive electrode active layer formed on the surface of the current collector, wherein the positive electrode active layer contains the aforementioned phosphate-based positive electrode material. The positive electrode of this application, due to the use of the aforementioned phosphate-based positive electrode material in the positive electrode active layer, improves the energy density, cycle life, and other electrochemical performance of the positive electrode.

[0123] In some possible implementations, the preparation of the positive electrode active layer includes the following steps: mixing the above-mentioned phosphate-based positive electrode material, conductive agent and binder to form an electrode slurry, coating the electrode slurry onto the current collector, and then preparing the positive electrode sheet through steps such as drying, rolling and die cutting.

[0124] In some possible implementations, the mass percentage of phosphate-based cathode material in the cathode active layer of the cathode sheet is 90% to 95%. Specifically, the mass percentage of phosphate-based cathode material in the cathode active material layer can be 90%, 91%, 92%, 93%, 94%, 95%, etc.

[0125] In some possible implementations, the current collector of the positive electrode includes, but is not limited to, any one of copper foil or aluminum foil.

[0126] In some possible implementations, the binder content in the positive electrode active material layer is 2wt% to 5wt%. In specific embodiments, the binder content can be typical but not limited to 2wt%, 3wt%, 4wt%, 5wt%, etc.

[0127] In some possible implementations, the binder includes one or more of the following: polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0128] In some possible implementations, the conductive agent content in the positive electrode active material layer is 1 wt% to 5 wt%. In specific embodiments, the conductive agent content can be a typical but not limited content such as 3 wt%, 4 wt%, or 5 wt%.

[0129] In some possible implementations, the conductive agent includes graphite, carbon black, acetylene black, graphene, carbon fiber, and C. 60 And one or more of carbon nanotubes.

[0130] In some possible implementations, a secondary battery is provided, which includes the aforementioned positive electrode. The secondary battery provided in this application, due to including the aforementioned positive electrode with excellent electrochemical performance such as high energy density and long cycle life, improves the energy density, cycle stability, and other electrochemical performance of the secondary battery.

[0131] This application does not specifically limit the negative electrode, electrolyte, separator, etc. in the secondary battery of the embodiments, and can be applied to any battery system.

[0132] In some possible implementations, the negative electrode active material of the secondary battery includes, but is not limited to, carbon materials such as graphite, soft carbon (e.g., coke), and hard carbon, or nitrides, tin-based oxides, tin alloys, and nano-anode materials. The current collector includes, but is not limited to, any one of copper foil and aluminum foil.

[0133] In some possible implementations, the steps for making the negative electrode sheet include: mixing the negative electrode active material with conductive agents such as conductive carbon black, binders such as carboxymethyl cellulose and styrene-butadiene rubber, and solvents such as water in a mass ratio of (80-99):(1-5):(2-10):100 to form a negative electrode slurry, then degassing under vacuum, discharging the material, coating it on a coating machine, and obtaining the negative electrode sheet after rolling, slitting, and die-cutting.

[0134] In some possible implementations, the membrane is capable of blocking electrons while allowing ions to pass through. Exemplary membranes include, but are not limited to, at least one material selected from polypropylene fibers, polyacrylonitrile fibers, polyvinyl formal fibers, poly(ethylene glycol terephthalate), polyethylene terephthalate, polyamide fibers, and poly(p-phenylene terephthalamide).

[0135] In some possible implementations, the electrolyte comprises at least one soluble metal salt. In some specific embodiments, the metal salt includes LiClO4, LiBF4, LiPF6, LiAsF6, LiCF3SO3, LiTDI, Li[(CF3SO2)2N], Li[(FSO2)2N], Li[(C m F 2m+1 SO2)(C n F 2n+1 At least one of SO2(N)[m, n], where m and n are natural numbers. These electrolytic salts can ensure high ionic conductivity of the electrolyte and do not undergo harmful side reactions with electrode materials, electrolyte, diaphragm, etc., and have good chemical stability.

[0136] In some possible implementations, the secondary battery includes at least one of a battery cell, a battery module, and a battery pack.

[0137] In some possible implementations, the battery cell types include lithium-ion batteries, as well as novel batteries such as lithium-air batteries and lithium metal batteries.

[0138] In some possible implementations, the battery cells of this application can be assembled into a battery module. The battery module can contain multiple battery cells, the specific number of which can be adjusted according to the application and capacity of the battery module. Furthermore, the battery module may also include a housing with a receiving space in which multiple battery cells are received.

[0139] In one possible implementation, battery cells and / or battery modules can also be assembled into a battery pack, and the number of battery cells or battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0140] To enable those skilled in the art to clearly understand the above-described implementation details and operations of this application, and to demonstrate the significant improvement in the performance of the method for determining iron phosphide in phosphate-based cathode materials in the embodiments of this application, the above technical solutions are illustrated below through multiple embodiments.

[0141] Example 1

[0142] A method for quantitative determination of trace Fe2P in lithium iron phosphate for lithium-ion batteries includes the following steps:

[0143] S1. Plotting the standard curve:

[0144] (1) Add 2g of sodium dodecyl sulfate to a 10L mixing tank containing 5L of demagnetizing water, place the mixing tank in a roller mixer and stir continuously for 15 minutes to fully dissolve the sodium dodecyl sulfate; add 1kg of lithium iron phosphate without iron phosphate and 0.00025g of Fe2P to the mixing tank to obtain standard solution 1.

[0145] (2) Place the magnetic rod wrapped in heat-shrink tubing into standard solution 1, and place the mixing bowl in a roller mixer to continuously stir for 30 minutes to adsorb magnetic material. After the stirring is complete, remove the magnetic rod with heat-shrink tubing and place it in a clean beaker. Remove the magnetic rod from the heat-shrink tubing and cut the heat-shrink tubing into three equal parts with ceramic scissors. Add demagnetizing water to the beaker, covering the heat-shrink tubing, and perform ultrasonic cleaning for 5 minutes. After cleaning, rinse the magnetic material on the heat-shrink tubing into the beaker with deionized water, while scraping off the magnetic material from the heat-shrink tubing with a ceramic knife. Place the rinsed heat-shrink tubing into another beaker, add water to cover the heat-shrink tubing, and ultrasonically clean for 5 minutes. Repeat the operation. Slowly pour the water mixture of magnetic material from all the beakers into another beaker, and use a magnetic block to perform magnetic separation at the bottom of the beaker. After all the magnetic material has been magnetically separated, add 4% dilute hydrochloric acid to the magnetic material to clean the lithium iron phosphate, thus obtaining the magnetic material.

[0146] (3) After the magnetic material was completely dissolved by heating 20 mL of aqua regia (1+1) (the volume ratio of aqua regia to water is 1:1, the concentration of nitric acid is 25.5%, and the concentration of hydrochloric acid is 4.5%) to 200℃, water was added to 100 mL, and the mixture was heated to 210℃ and boiled. Quinomolybdate reagent was added to react and generate quinoline phosphomolybdate precipitate. The mass of the precipitate was recorded.

[0147] (4) Repeat steps (1) to (3) sequentially, changing the mass of Fe2P in the standard solution to 0.0005 g, 0.001 g, 0.003 g, 0.005 g, 0.007 g, 0.010 g, and 0.015 g, respectively, and determine the corresponding mass of quinoline phosphomolybdate precipitate in the standard solutions with different Fe2P concentrations. The mass of Fe2P in the standard solution shows a certain linear relationship with the mass of quinoline phosphomolybdate precipitate. A standard curve is plotted with Fe2P as the abscissa and the mass of quinoline phosphomolybdate precipitate as the ordinate, as shown in the attached figure. Figure 3 As shown, the linear relationship is R 2 =0.9996.

[0148] S2. Sample testing:

[0149] The test solution was prepared, and the difference between the test solution and the standard solution was that the lithium iron phosphate without iron phosphate was replaced with an equal amount of the test lithium iron phosphate, and no Fe2P was added to the test solution. The test process and conditions for obtaining the corresponding quinoline phosphomolybdate precipitate in the test solution were consistent with the determination process in steps (1) to (3) of the standard curve. After measuring the mass of the quinoline phosphomolybdate precipitate, the mass of the quinoline phosphomolybdate precipitate was substituted into the standard curve in step (4), and the content of iron phosphate in 1 kg of the test lithium iron phosphate was calculated to be 0.00115 g.

[0150] Example 2

[0151] A method for quantitative determination of trace Fe2P in lithium iron phosphate for lithium-ion batteries includes the following steps:

[0152] S1. Plotting the standard curve:

[0153] (1) Add 1.9g of sodium dodecyl sulfate to a 10L mixing tank containing 5L of demagnetizing water, place the mixing tank in a roller mixer and stir continuously for 13 minutes to fully dissolve the sodium dodecyl sulfate; add 1.01kg of lithium iron phosphate without iron phosphate and 0.00025g of Fe2P to the mixing tank to obtain standard solution 1.

[0154] (2) Place a magnetic rod wrapped in heat-shrink tubing into standard solution 1. Place the mixing tank in a roller mixer and stir continuously for 28 minutes to adsorb magnetic material. After the stirring is complete, remove the magnetic rod with heat-shrink tubing and place it in a clean beaker. Remove the magnetic rod from the heat-shrink tubing and cut the heat-shrink tubing into three equal parts with ceramic scissors. Add demagnetizing water to the beaker, covering the heat-shrink tubing, and perform ultrasonic cleaning for 6 minutes. After cleaning, rinse the magnetic material on the heat-shrink tubing into the beaker with deionized water. At the same time, scrape the magnetic material off the heat-shrink tubing with a ceramic knife. Place the rinsed heat-shrink tubing into another beaker, add water to cover the heat-shrink tubing, and ultrasonically clean for 6 minutes. Repeat the operation. Slowly pour the water mixture of magnetic material from all beakers into another beaker. Use a magnetic block to perform magnetic separation at the bottom of the beaker. After all the magnetic material has been magnetically separated, add 4% dilute hydrochloric acid to the magnetic material to clean the lithium iron phosphate, obtaining the magnetic material.

[0155] (3) After the magnetic material was completely dissolved by heating 20 mL of aqua regia (1+1) (the volume ratio of aqua regia to water is 1:1, the concentration of nitric acid is 25.5%, and the concentration of hydrochloric acid is 4.5%) to 200℃, water was added to 100 mL, and the mixture was heated to 210℃ and boiled. Quinomolybdate reagent was added to react and generate quinoline phosphomolybdate precipitate. The mass of the precipitate was recorded.

[0156] (4) Repeat steps (1) to (3) sequentially, changing the mass of Fe2P in the standard solution to 0.0005 g, 0.001 g, 0.003 g, 0.005 g, 0.007 g, 0.010 g, and 0.015 g, respectively, and measuring the corresponding mass of quinoline phosphomolybdate precipitate in the standard solutions with different Fe2P concentrations. The mass of Fe2P in the standard solution shows a certain linear relationship with the mass of quinoline phosphomolybdate precipitate. A standard curve is plotted with Fe2P as the abscissa and the mass of quinoline phosphomolybdate precipitate as the ordinate. The linear relationship is R0. 2 =0.9995.

[0157] S2. Sample testing:

[0158] The test solution was prepared, and the difference between the test solution and the standard solution was that the lithium iron phosphate without iron phosphate was replaced with an equal amount of the lithium iron phosphate to be tested, and no Fe2P was added to the test solution. The test process and conditions for obtaining the corresponding quinoline phosphomolybdate precipitate in the test solution were consistent with the determination process in steps (1) to (3) of the standard curve. After measuring the mass of the quinoline phosphomolybdate precipitate, the mass of the quinoline phosphomolybdate precipitate was substituted into the standard curve in step (4), and the content of iron phosphate in 1 kg of lithium iron phosphate to be tested was calculated to be 0.00114 g.

[0159] Example 3

[0160] A method for quantitative determination of trace Fe2P in lithium iron phosphate for lithium-ion batteries includes the following steps:

[0161] S1. Plotting the standard curve:

[0162] (1) Add 2.1g of sodium dodecyl sulfate to a 10L mixing tank containing 5.1L of demagnetizing water, place the mixing tank in a roller mixer and stir continuously for 14 minutes to fully dissolve the sodium dodecyl sulfate; add 1.02kg of lithium iron phosphate without iron phosphate and 0.00025g of Fe2P to the mixing tank to obtain standard solution 1.

[0163] (2) Place the magnetic rod wrapped in heat-shrink tubing into standard solution 1, and place the mixing tank in a roller mixer to continuously stir for 31 minutes to adsorb magnetic material. After the stirring is complete, remove the magnetic rod with heat-shrink tubing and place it in a clean beaker. Remove the magnetic rod from the heat-shrink tubing and cut the heat-shrink tubing into three equal parts with ceramic scissors. Add demagnetizing water to the beaker, covering the heat-shrink tubing, and perform ultrasonic cleaning for 6 minutes. After cleaning, rinse the magnetic material on the heat-shrink tubing into the beaker with deionized water, while scraping off the magnetic material from the heat-shrink tubing with a ceramic knife. Place the rinsed heat-shrink tubing into another beaker, add water to cover the heat-shrink tubing, and ultrasonically clean for 4 minutes. Repeat the operation. Slowly pour the water mixture of magnetic material from all the beakers into another beaker, and use a magnetic block to perform magnetic separation at the bottom of the beaker. After all the magnetic material has been magnetically separated, add 4% dilute hydrochloric acid to the magnetic material to clean the lithium iron phosphate, thus obtaining the magnetic material.

[0164] (3) After the magnetic material was completely dissolved by heating 18 mL of aqua regia (1+1) (the volume ratio of aqua regia to water is 1:1, the concentration of nitric acid is 25.5%, and the concentration of hydrochloric acid is 4.5%) to 200℃, water was added to 100 mL, and the mixture was heated to 210℃ and boiled. Quinomolybdate reagent was added to react and generate quinoline phosphomolybdate precipitate. The mass of the precipitate was recorded.

[0165] (4) Repeat steps (1) to (3) sequentially, changing the mass of Fe2P in the standard solution to 0.0005 g, 0.001 g, 0.003 g, 0.005 g, 0.007 g, 0.010 g, and 0.015 g, respectively, and measuring the corresponding mass of quinoline phosphomolybdate precipitate in the standard solutions with different Fe2P concentrations. The mass of Fe2P in the standard solution shows a certain linear relationship with the mass of quinoline phosphomolybdate precipitate. A standard curve is plotted with Fe2P as the abscissa and the mass of quinoline phosphomolybdate precipitate as the ordinate. The linear relationship is R0. 2 =0.9993.

[0166] S2. Sample testing:

[0167] The test solution was prepared, and the difference between the test solution and the standard solution was that the lithium iron phosphate without iron phosphate was replaced with an equal amount of the test lithium iron phosphate, and no Fe2P was added to the test solution. The test process and conditions for obtaining the corresponding quinoline phosphomolybdate precipitate in the test solution were consistent with the determination process in steps (1) to (3) of the standard curve. After measuring the mass of the quinoline phosphomolybdate precipitate, the mass of the quinoline phosphomolybdate precipitate was substituted into the standard curve in step (4), and the content of iron phosphate in 1 kg of the test lithium iron phosphate was calculated to be 0.00115 g.

[0168] Example 4 [The difference from Example 1 is the addition of 5g of sodium dodecyl sulfate]

[0169] A method for quantitative determination of trace Fe2P in lithium iron phosphate for lithium-ion batteries includes the following steps:

[0170] S1. Plotting the standard curve:

[0171] (1) Add 5g of sodium dodecyl sulfate to a 10L mixing tank containing 5L of demagnetizing water, place the mixing tank in a roller mixer and stir continuously for 15 minutes to fully dissolve the sodium dodecyl sulfate; add 1kg of lithium iron phosphate without iron phosphate and 0.00025g of Fe2P to the mixing tank to obtain standard solution 1.

[0172] (2) Place the magnetic rod wrapped in heat-shrink tubing into standard solution 1, and place the mixing bowl in a roller mixer to continuously stir for 30 minutes to adsorb magnetic material. After the stirring is complete, remove the magnetic rod with heat-shrink tubing and place it in a clean beaker. Remove the magnetic rod from the heat-shrink tubing and cut the heat-shrink tubing into three equal parts with ceramic scissors. Add demagnetizing water to the beaker, covering the heat-shrink tubing, and perform ultrasonic cleaning for 5 minutes. After cleaning, rinse the magnetic material on the heat-shrink tubing into the beaker with deionized water, while scraping off the magnetic material from the heat-shrink tubing with a ceramic knife. Place the rinsed heat-shrink tubing into another beaker, add water to cover the heat-shrink tubing, and ultrasonically clean for 5 minutes. Repeat the operation. Slowly pour the water mixture of magnetic material from all the beakers into another beaker, and use a magnetic block to perform magnetic separation at the bottom of the beaker. After all the magnetic material has been magnetically separated, add 4% dilute hydrochloric acid to the magnetic material to clean the lithium iron phosphate, thus obtaining the magnetic material.

[0173] (3) After the magnetic material was completely dissolved by heating 20 mL of aqua regia (1+1) (the volume ratio of aqua regia to water is 1:1, the concentration of nitric acid is 25.5%, and the concentration of hydrochloric acid is 4.5%) to 200℃, water was added to 100 mL, and the mixture was heated to 210℃ and boiled. Quinomolybdate reagent was added to react and generate quinoline phosphomolybdate precipitate. The mass of the precipitate was recorded.

[0174] (4) Repeat steps (1) to (3) sequentially, changing the mass of Fe2P in the standard solution to 0.0005 g, 0.001 g, 0.003 g, 0.005 g, 0.007 g, 0.010 g, and 0.015 g, respectively, and determine the corresponding mass of quinoline phosphomolybdate precipitate in the standard solutions with different Fe2P concentrations. The mass of Fe2P in the standard solution shows a certain linear relationship with the mass of quinoline phosphomolybdate precipitate. A standard curve is plotted with Fe2P as the abscissa and the mass of quinoline phosphomolybdate precipitate as the ordinate, as shown in the attached figure. Figure 4 As shown, the linear relationship is R 2 =0.9950.

[0175] S2. Sample testing:

[0176] The test solution was prepared, and the difference between the test solution and the standard solution was that the lithium iron phosphate without iron phosphate was replaced with an equal amount of the test lithium iron phosphate, and no Fe2P was added to the test solution. The test process and conditions for obtaining the corresponding quinoline phosphomolybdate precipitate in the test solution were consistent with the determination process in steps (1) to (3) of the standard curve. After measuring the mass of the quinoline phosphomolybdate precipitate, the mass of the quinoline phosphomolybdate precipitate was substituted into the standard curve in step (4), and the content of iron phosphate in 1 kg of the test lithium iron phosphate was calculated to be 0.00185 g.

[0177] Comparative Example 1

[0178] A method for quantitative determination of trace Fe2P in lithium iron phosphate for lithium-ion batteries is disclosed, differing from Example 1 in that no dispersant is added to the standard solution and the test solution. Other operating steps are the same as in Example 1. The standard curve is shown in the attached figure. Figure 5 As shown, the linear relationship is R 2 =0.9843. The calculated content of iron phosphide in 1 kg of lithium iron phosphate is 0.00091.

[0179] Comparative Example 2 [Blank Control Group]

[0180] A quantitative determination method for trace Fe2P in lithium iron phosphate for lithium-ion batteries, which differs from Example 1 in that: in step S2, no lithium iron phosphate is added to the sample for testing, and the mass of quinoline phosphomolybdate precipitate obtained during the experiment is 0g, that is, the content of iron phosphide in Comparative Example 2 is 0g.

[0181] The results of the iron phosphide content determination in each example and comparative example are shown in Table 1 below:

[0182] Table 1

[0183]

[0184] Furthermore, to verify the progressiveness of the embodiments of this application, the standard curves plotted for Embodiments 1, 4, and Comparative Example 1 are compared, as shown in the appendix. Figure 6 As shown, the standard curve in Example 1 has the best linear fit, while the standard curve in Comparative Example 1 has a significantly lower fit than that in Example 1. In Example 4, due to the excessive amount of dispersant added, the high concentration generated more bubbles, increasing the error during the extraction of magnetic materials, thus resulting in a lower standard curve fit than in Example 1.

[0185] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for determining iron phosphide in phosphate-based cathode materials, characterized in that, Includes the following steps: Prepare a series of standard solutions of phosphate-based cathode materials with different iron phosphide contents; The magnetic substances in the standard solutions were collected and purified separately. After digestion of the magnetic substances in the standard solutions, quinoline phosphomolybdate reagent was added to carry out a precipitation reaction to obtain the quinoline phosphomolybdate precipitate in the standard solutions. A standard curve was plotted based on the mass of ferric phosphide in the standard solutions with different ferric phosphide contents and the mass of quinoline phosphomolybdate precipitate in the standard solutions. A test solution containing the phosphate-based cathode material to be tested was prepared. Magnetic substances in the test solution were collected and purified. After digesting the magnetic substances in the test solution, quinoline phosphomolybdate reagent was added to carry out a precipitation reaction to obtain quinoline phosphomolybdate precipitate in the test solution. The mass of quinoline phosphomolybdate precipitate in the test solution was determined, and the content of iron phosphide in the phosphate-based cathode material was calculated based on the standard curve.

2. The method for determining iron phosphide in phosphate-based cathode materials as described in claim 1, characterized in that, The standard solution contains phosphate-based cathode material without ferric phosphate, ferric phosphate, dispersant, and demagnetizing water; And / or, the test solution contains the phosphate-based cathode material to be tested, a dispersant, and demagnetizing water; And / or, the concentration and type of the phosphate-based cathode material in the test solution are the same as the concentration and type of the phosphate-based cathode material in the standard solution; And / or, the determination conditions for quinoline phosphomolybdate precipitate in the test solution are the same as the determination conditions for the corresponding quinoline phosphomolybdate precipitate in the standard solution; And / or, prepare the standard solutions with at least five iron phosphide concentration gradients; And / or, the concentration of ferric phosphide in the standard solution is 0.00025 g / L to 0.015 g / L.

3. The method for determining iron phosphide in phosphate-based cathode materials as described in claim 2, characterized in that, The concentration and type of dispersant in the test solution are the same as those in the standard solution; And / or, in the standard solution and the test solution, the dispersant includes at least one of sodium dodecyl sulfate, vinylpyrrolidone, hexadecyltrimethylammonium bromide, and Huntsman X-3204; And / or, in the standard solution and the test solution, the concentration of the dispersant is 0.36 g / L to 0.5 g / L; And / or, in the standard solution, the concentration of the phosphate-free iron phosphate cathode material is 0.198 kg / L to 0.22 kg / L; And / or, in the test solution, the concentration of the phosphate-based cathode material to be tested is 0.198 kg / L to 0.22 kg / L; And / or, in the phosphorus-free iron phosphate cathode material and the phosphate cathode material to be tested, the phosphate cathode material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium titanium phosphate, lithium manganese phosphate, lithium manganese iron titanium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

4. The method for determining iron phosphide in phosphate-based cathode materials as described in claim 3, characterized in that, The step of collecting and purifying the magnetic material in the standard solution or the test solution includes: using a magnetic rod to adsorb the standard solution or the test solution, collecting the magnetic material adsorbed on the surface of the magnetic rod, and performing magnetic separation and washing treatments in sequence to obtain the magnetic material in the standard solution or the test solution. And / or, the step of digesting the magnetic material in the standard solution or the test solution includes: dissolving the magnetic material in an acidic solution under heating conditions; And / or, when determining the quinoline phosphomolybdate precipitate in the standard solution or the test solution, the temperature conditions for the precipitation reaction are 200℃~220℃; And / or, the standard curve is plotted with the mass of ferric phosphide on the x-axis and the mass of quinoline phosphomolybdate precipitate on the y-axis.

5. The method for determining iron phosphide in phosphate-based cathode materials as described in claim 4, characterized in that, The magnetic rod is wrapped in heat shrink tubing. After the adsorption treatment, the magnetic rod wrapped in heat shrink tubing is disassembled and the magnetic material on the surface of the heat shrink tubing is collected. And / or, the stirring speed of the adsorption treatment is 50 rpm to 70 rpm, and the stirring time is 25 min to 35 min; And / or, the magnetic separation process includes the steps of: using a magnetic block to perform non-contact sorting of the collected magnetic material to separate and remove phosphate-based cathode materials; And / or, the washing process includes the steps of: washing the magnetic material after magnetic separation with dilute hydrochloric acid at a concentration of 4% to 6% to separate and remove the phosphate-based cathode material; And / or, the concentration of nitric acid in the acidic solution is 25% to 30%, and the concentration of hydrochloric acid is 4% to 10%; And / or, the volume ratio of the acidic solution to the quinomolybdate reagent is (18 mL to 25 mL): (28 mL to 33 mL); And / or, the temperature of the heating conditions is 200℃~240℃.

6. The method for determining iron phosphide in phosphate-based cathode materials as described in claim 5, characterized in that, The magnetic rod is selected from the model of 11000GS to 12000GS; And / or, in the magnetic rod wrapped by the heat shrink tubing, the heat shrink tubing is made of at least one of polypropylene, polyvinyl fluoride, ethylene propylene diene monomer (EPDM), and polytetrafluoroethylene (PTFE). And / or, the acidic solution comprises aqua regia and water in a volume ratio of 1:

1.

7. The method for determining iron phosphide in phosphate-based cathode materials according to any one of claims 1 to 6, characterized in that, The linear correlation coefficient R of the standard curve 2 Not less than 0.

999.

8. A positive electrode material, characterized in that, The cathode material contains a phosphate-based cathode material. After determining the iron phosphide content using the method described in any one of claims 1 to 7, the iron phosphide content in the phosphate-based cathode material is adjusted.

9. The cathode material as described in claim 8, characterized in that, The content of iron phosphide in the phosphate-based cathode material is no higher than 5 ppm; And / or, methods for regulating the iron phosphide content in the phosphate-based cathode material include at least one of: controlling process conditions, physical adsorption removal, and chemical dissolution removal.

10. An application of a positive electrode material, characterized in that, The cathode material as described in any one of claims 8 to 9 is applied to cathode sheets and / or secondary batteries.

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